1. Field of the Invention
The present invention relates to rodless cylinders and more specifically to a rodless cylinder characterized by the shape of its bore.
2. Description of the Related Art
A rodless cylinder is conventionally employed as a transfer device for a workpiece in a factory or the like. The rodless cylinder has a shorter length than a cylinder having a rod, considering a displacement length. Therefore, the rodless cylinder occupies a smaller area, is easy to handle and allows a high level positioning operation or the like.
The rodless cylinder mainly includes a cylinder tube having a bore, a piston provided in the bore, and a slide table coupled to the piston to reciprocate along the cylinder tube with the movement of the piston. In this case, the bore is formed to have an approximately circular cross section.
Meanwhile, there has been a demand for reducing the thickness of the rodless cylinders. However, the space for forming the bore must be secured in the cylinder tube, which makes it difficult to reduce the thickness of the rodless cylinder having the bore with an approximately circular cross section.
Thus, rodless cylinders having a bore with an approximately oval or ellipse cross section have been developed and reduced to practice in order to provide rodless cylinders with a reduced thickness.
However, in such a cylinder tube having a bore with an approximately oval or ellipse cross section, the rigidity thereof is likely to be reduced if a thickness of the cylinder tube or an ellipticity relating to a cross sectional shape of the bore would not be suitable. Further, in the cylinder tube having a bore with an approximately oval or ellipse cross section, it is difficult to provide centralized piping through the cylinder tube when thinned portions are formed on the cylinder tube.
It is a general object of the invention to provide a rodless cylinder having a reduced thickness while maintaining high rigidity.
It is a main object of the invention to provide a rodless cylinder with a reduced thickness while securing a space to form a fluid bypass passage.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.